Explore surfplot as another plotting backend

https://surfplot.readthedocs.io/en/latest/index.html

Open questions:

- nltools is primarily for volumetric data so we'll need to see how projection interacts with our brainspace template resolutions
- how does this affect our wasm build and should it be an optional install (eg vtk)
- what should the user api look like given existing BrainData plotting methods

Start by reading the surfplot documentation and the existing BrainData plotting methods. Investigate how projection interacts with brainspace template resolutions and how a surfplot backend would affect the wasm build and optional installation alongside vtk. Done requires a settled user API and an implementation plan for the backend.

Written by the indexing model from the issue text.